This project involves the design, development and integration of a new active limb sounding method modeled after the successful Global Positioning System (GPS) Radio Occultation (RO) sounding technique. The difference is that the new method is not constrained to operate with radio frequency sources specifically allocated for GPS applications. Instead, source frequencies in the microwave are chosen relatively close to atmospheric absorption lines in order to maximize detection of single atmospheric constituents, such as water vapor. Both sender and receiver operate on those frequencies. The operational concept is low Earth orbiting (LEO) satellite platforms flying both transmitter and receiver, each occulting one another.
The project is called The Active Temperature, Ozone and Moisture Microwave Spectrometer (ATOMMS). In theory, ATOMMS will profile tropospheric and middle atmosphere water vapor and middle atmosphere ozone to 1-5%, temperature to 0.5K, and geopotential heights to 10-20 m, all with ~200 m vertical resolution, in both clear and cloudy air. This performance will improve significantly with averaging. ATOMMS is self-calibrating, which eliminates long-term drift. The success of this project is a necessary step toward space-based LEO ATOMMS measurements.
The Principal Investigator (PI) is modifying his earlier ATOMMS design by increasing the number of high band tones from 2 to 4, upgrading the instrument electronics and making commensurate changes in the retrieval system. These upgrades will provide the information needed to isolate, quantify and mitigate several recently recognized key sources of error. With 4 high band tones, the PI will be able to investigate and hopefully explain any discrepancies and surprises that are to be expected in a first time measurement demonstration such as this. Specifically, the 4 high band tones will provide the information to (i) isolate and reduce amplitude scintillations due to turbulent fluctuations in the imaginary and real refractivity, (ii) quantify and reduce residual biases left after incomplete removal of ice cloud scattering using only two tones, and (iii) quantify errors in spectroscopy that are otherwise likely to limit the accuracy of ATOMMS-derived profiles. In addition, 4 high band tones will increase the likelihood of acquiring useful measurements even if a tone were to fail during a flight and allow the PI to demonstrate profiling N2O and H3NO and the 18O/16O isotopic ratio of water vapor. Without the information from four channels of high band data in the aircraft to aircraft demonstrations the PI would be unable to quantify several critical errors leaving the assessment of ATOMMS incomplete and its ultimate performance uncertain.
ATOMMS observations will fulfill crucial needs for atmospheric, climate and geospace scientists, by providing new sources of global, high vertical resolution, highly stable and accurate data important to their research. The observations will serve mission agencies in weather and chemical weather forecasting and would be a key element in the international Global Climate Observing System (GCOS). In regard to education and training, several junior scientists, including the co-PI, will help to conduct this research.
